Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

012
FXUS63 KLOT 030804
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
304 AM CDT Sun May 3 2026

.KEY MESSAGES...

- A period of rain showers and breezy southwesterly winds are
  expected today.

- Showers and scattered thunderstorms are likely late Monday
  into Tuesday. A few storms Monday night could be strong to
  severe with threats for hail and strong winds (mainly south of
  I-80).

- Outside of a brief warmup today into Monday, near to below
  normal temperatures are favored through next weekend with
  occasional chances for rain showers.

&&

.DISCUSSION...
Issued at 303 AM CDT Sun May 3 2026

A fairly tame upper-level shortwave trough is evident in GOES
water vapor imagery early this morning over southern Minnesota.
This shortwave will proceed southeastward through the remainder
of the morning and arrive in northern Illinois a bit after
sunrise, accompanied by some rain showers. The earlier 00Z MPX,
DVN, and ILX RAOBs all sampled a notable wedge of dry air below
700 mb in the air mass downstream of the shortwave, and the
forcing provided by the shortwave alone won`t be enough to
substantially alter this dry low-level air. However, low- to
mid-level frontogenesis and isentropic lift will create a
focused zone of enhanced ascent that should induce enough
hydrometeor mass for more appreciable top-down saturation to be
realized, making it more likely for measurable rainfall to be
observed across a corridor or two of our forecast area. That
said, the dry sub-cloud air and relatively short duration of
the precipitation will largely keep rainfall totals under a
tenth of an inch, with some areas likely to not see any
measurable rainfall too.

After these showers depart this afternoon (possibly as early as
the late morning across our western and far northern counties),
already breezy southwesterly winds -- induced by a compressed
pressure gradient between the cold frontal surface trough and a
~1020 mb surface high centered over the southeastern CONUS --
will pick up even further as mixing heights rise into stronger
750-850 mb flow. This will likely result in a period of 30-40
mph gusts prior to this stronger low-level flow advancing off to
the east and the onset of nocturnal boundary layer
stabilization. These winds will help usher in more seasonable
temperatures for early May into our area with today`s high
temperatures expected to range from the low 60s to near 70F.

The southwesterly breezes will continue into Monday as a deeper
surface low associated with a more pronounced upper-level
trough dives southeastward from the Canadian Prairies towards
Lake Superior. Continued warm air advection off of these winds
will propel temperatures well into the 70s south of another
inbound cold front. The aggressively-mixed HRRR and RAP actually
both have a good chunk of the area climbing above 80F tomorrow,
and this outcome appears to be conceivable given the tendency
for temperatures to overperform in these breezy warm air
advection regimes with deep mixing and mostly clear skies. That
said, would like to see how much dew points mix out and how
temperatures commensurately perform in the upstream source
region for Monday`s air mass before fully biting on this more
extreme/outlying forecast solution.

An influx of better (though still far from stellar) low-level
moisture will accompany the arrival of the warmer temperatures
on Monday, making conditions more favorable for showers and
thunderstorms to occur. There appear to be two main
areas/forcing mechanisms that we`ll need to monitor for
convection late Monday afternoon and evening. One area will be
along the aforementioned cold front. There is fairly good
agreement amongst the 00Z HREF members that convection will
bubble within a narrow axis of meager MLCAPE along the cold
front while it is in Iowa and Wisconsin during the afternoon.
However, the front likely won`t reach our northern counties
until around sunset, by which point, the already limited
instability will be on a downward trend, putting into question
how long this frontal convection will be able to sustain itself
into our forecast area during the evening.

Additionally, a southwest-northeast oriented low-level jet
centered just to our south/southeast and juxtaposed by better
low-level moisture and instability will likely try to force
convection in or near our southern counties as it strengthens
during the evening. Eventually, the cold front will encounter
the slightly higher dew points across our southern CWA and cross
paths with the low-level jet, but this likely won`t happen
until late in the evening or during the early overnight hours --
by which point, the available instability coincident with the
better moisture will have likely dwindled quite a bit. If storms
are able to occur in our area while sufficient instability
remains, then 30-40 kts of deep-layer shear would support the
potential for some degree of storm organization and an attendant
threat for hail and strong to locally damaging winds. This
would primarily be the case with any storms near the low-level
jet in the southern half of our CWA, but the early evening cold
frontal convection may still produce some gusty outflow winds in
our northern counties prior to petering out.

All that said, while some finer-scale forecast details remain
uncertain (particularly with respect to the threat for severe
weather), confidence in showers and thunderstorms occurring in
our area on Monday night has increased with pretty much every
forecast model resolving at least scattered convection in our
forecast area in spite of the somewhat limited moisture. PoPs
for Monday night have been brought up into the "likely" range
in response. With the frontal zone not expected to clear our
area all that quickly and more abundant large-scale forcing
expected to arrive on the scene, showers and storms will likely
continue into the daytime on Tuesday with the greatest
coverage/chances focused in our southern counties, which will be
closer to the surface front. The extended period of rainfall
(including some potential for training convection with locally
heavier rainfall rates late Monday night/early Tuesday morning)
may give us some things to monitor on the hydrologic front, but
at this time, think that any hydrologic issues that arise would
be more of the nuisance variety and fairly limited in scope.

Aggregate troughing and northwest flow over the Great Lakes and
Midwest will then be the theme for the synoptic upper-level
pattern for the latter half of the week and into next weekend.
This will favor the persistence of near to below normal
temperatures and should allow for additional periodic
opportunities for rain showers in the coming days as more
disturbances embedded within the mean longwave troughing and
northwesterly flow aloft dive into the region.

Ogorek

&&

.AVIATION /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 1239 AM CDT Sun May 3 2026

- Strong and gusty south-southwest winds are expected today,
  especially this afternoon.

Scattered showers will move across the region later this morning
in association with an upper level disturbance. Given the that
coverage of the showers could be somewhat limited and the
possibility for virga with the low level dry air, opted to just
hang onto the PROB30 for now. Even during any -SHRA that would
impact a terminal, I`d expect conditions to remain VFR.

South-southwest winds will increase and become gusty after
sunrise, with magnitude of gusts and sustained winds likely
continuing to ramp up late morning into the early afternoon.
During the afternoon prevailing gusts over 30kt are likely
with a few rogue gusts approaching 40kt possible, especially if
with any more prominent breaks in the cloudiness. Winds will
begin to ease prior to sunset with gusts likely abating by
around sunset. Light south-southwest winds expected by mid-late
evening through the overnight.

- Izzi

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 7 AM this morning to 7 PM CDT this
     evening for the IL and IN nearshore waters.

&&

$$

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